1. Field of the Invention
The invention relates to a sealing structure of an electroluminescent display device for improving moisture resistance.
2. Description of the Related Art
In recent years, organic electroluminescent (hereafter, referred to as EL) display devices with organic El elements, which are a self-emission device, has been receiving an attention as a new display device replacing CRT and LCD displays.
Since the organic El element is sensitive to moisture, in an organic EL display panel, a structure in which the organic El element is covered with a metal cap or a glass cap coated with a desiccant has been proposed. FIG. 6 is a cross-sectional view showing such a conventional structure of the organic EL display panel.
A device glass substrate 70 has a display region having many organic El elements 71 on its surface. The device glass substrate 70 is attached to a sealing glass substrate 80 for sealing the devices with sealing resin 75 made of an epoxy resin or the like. The sealing glass substrate 80 has a concave portion 81 (hereafter, referred to as a pocket portion 81) in a region corresponding to the display region, which is formed by etching. The pocket portion 81 is coated with a desiccant layer 82 for absorbing moisture on its bottom.
Here, forming of the desiccant layer 82 on the bottom of the pocket portion 81 is for securing a space between the desiccant layer 82 and the organic El element 71. This structure prevents the desiccant layer 82 from contacting the organic El element 71 and thus from damaging the organic El element 71.
It is necessary for the organic EL display panel to secure moisture resistance as well as reliability in resistance to temperature changes. We performed a temperature cycling test on organic EL panels, in which the temperature is raised and reduced in a cycle repeatedly. It was found that the desiccant layer 82 partially peeled off and came away from the sealing glass substrate 80 as shown in FIG. 7. It was also found that the desiccant layer 82 was partially peeled and torn and the torn portion 82A of the desiccant layer 82 rested between the desiccant layer 82 and the device glass substrate 70. If these peeling off events happen, it is likely that the organic EL element 71 is damaged